Proposals for the geological disposal of high-level radioactive waste incorporate bentonite as a buffer material around the waste canister. However, prolonged exposure to elevated temperatures may affect the buffer's performance. The HotBENT experiment was designed to investigate these potential effects by subjecting bentonite to sustained thermal loading of up to 200°C over two decades. To monitor buffer evolution before dismantling, numerous sensors were installed to collect continuous data. Building on insights from the pioneering FEBEX project, HotBENT data are compared with established processes in bentonite-based buffers at lower temperatures. After the relatively short period of 3.5 years, no qualitative evidence could be observed so far that might indicate additional processes ongoing in the bentonite buffer beyond those observed in lower-temperature experiments. However, long-term effects such as mineralogical changes or pore-space cementation—potentially detrimental to buffer performance—are expected to be detected only after partial or final dismantling.
Schneeberger et al. (Tue,) studied this question.